On Mon, 2017-12-04 at 16:09 +1100, Michael Ellerman wrote: > Nicholas Piggin <[email protected]> writes: > > > When an interrupt is returning to a soft-disabled context (which can > > happen for non-maskable interrupts or synchronous interrupts), it goes > > through the motions of soft-disabling again, including calling > > TRACE_DISABLE_INTS (i.e., trace_hardirqs_off()). > > > > This is not necessary, because we must already be soft-disabled in the > > interrupt context, it also may be causing crashes in the irq tracing > > code to re-enter as an nmi. Replace it with a warning to ensure that > > soft-interrupts are still disabled. > > > > Signed-off-by: Nicholas Piggin <[email protected]> > > --- > > arch/powerpc/kernel/entry_64.S | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > So this patch is the core of the bug fix I gather. > > Git blames says: > > Fixes: 7c0482e3d055 ("powerpc/irq: Fix another case of lazy IRQ state > getting out of sync") > Cc: [email protected] # v3.4+ > > But I'm wondering how this has been broken that long without us > noticing? You hit it doing some sort of perf stress test I think - so is > it just that we've never pushed hard enough? Or did something change to > expose this? Or we're just not sure?
We have some traps that do local_irq_enable ... you may want to double check instruction emu, page faults, alignment etc... I wouldn't be surprised if we have case where an interrupt "returns" soft enabled. > cheers > > > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S > > index 3320bcac7192..36878b6ee8b8 100644 > > --- a/arch/powerpc/kernel/entry_64.S > > +++ b/arch/powerpc/kernel/entry_64.S > > @@ -911,9 +911,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR) > > beq 1f > > rlwinm r7,r7,0,~PACA_IRQ_HARD_DIS > > stb r7,PACAIRQHAPPENED(r13) > > -1: li r0,0 > > - stb r0,PACASOFTIRQEN(r13); > > - TRACE_DISABLE_INTS > > +1: > > +#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_BUG) > > + /* The interrupt should not have soft enabled. */ > > + lbz r7,PACASOFTIRQEN(r13) > > +1: tdnei r7,0 > > + EMIT_BUG_ENTRY 1b,__FILE__,__LINE__,BUGFLAG_WARNING > > +#endif > > b .Ldo_restore > > > > /* > > -- > > 2.15.0
